msm: mdss: Reserve framebuffer memory for the splash screen

Reserve memory for the framebuffer in the HLOS partition that
would be used to display splash screen in the bootloader as
well as the initial stages of the kernel bootup. This avoids
copying splash screen memory to a local buffer in the kernel.
The reserved memory would be freed when the first real update
comes in from the userspace.

Change-Id: I7dc256f8ffd69c24e56ac10ed57e37d96c8c9a2f
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>